The present invention relates to a cathode ray tube, and in particular to a cathode ray tube capable of supporting an electron gun firmly within its neck portion.
Generally, an electron gun of a cathode ray tube is supported on a stem of the cathode ray tube and is fixed at a specified position within its neck portion by an electron gun supporting structure.
FIG. 5 is a schematic cross-sectional view of a conventional color cathode ray tube.
In FIG. 5, reference numeral 21 denotes a panel portion, 21F is a faceplate, 22 is a neck portion, 23 is a funnel portion, 24 is a phosphor screen, 25 is a shadow mask, 26 is an internal magnetic shield, 27 is a deflection yoke, 28 is a stem, 29 is a three-beam in-line type electron gun, 30 is an electron beam, and 50 is an internal graphite coating.
A (a glass bulb) vacuum envelope of the color cathode ray tube comprises the panel portion 21 having the generally rectangular faceplate 21F, the narrow cylindrical neck portion 22 housing the three-beam in-line type electron gun 29, and the generally truncated-cone shaped funnel portion 23 connecting the panel portion 21 and the neck portion 22. The phosphor screen 24 is formed on the inner surface of the faceplate 21F of the panel portion 21, and the shadow mask 25 having a large number of electron beam-transmissive apertures is fixed and closely spaced from the phosphor screen 24 within the panel portion 21. The internal magnetic shield 26 is disposed within the funnel portion 23, and the deflection yoke 27 is mounted around the outside of the funnel portion 23. The in-line type electron gun 29 is supported on the stem 28 by an electron gun supporting structure described subsequently, and three electron beams 30 (only one of which is shown in FIG. 5) emitted from the electron gun 29 are deflected and scanned horizontally and vertically by the deflection yoke 27, then pass through the electron beam-transmissive apertures in the shadow mask 25, and then impinge upon the phosphor screen 24.
The mechanism and operation of displaying a picture by the conventional cathode ray tube is well-known to those skilled in the art, and the explanation of those is omitted.
FIG. 6A is a broken-away side view of the neck portion 22 of the conventional color cathode ray tube housing the in-line type electron gun 29, FIG. 6B is an enlarged cross-sectional view of the neck portion 22 taken along line VIBxe2x80x94VIB of FIG. 6A, FIG. 6C is an enlarged cross-sectional view of a supporting member 36 taken along line VIBxe2x80x94VIB of FIG. 6A, and FIG. 6D is an enlarged cross-sectional view of the neck portion 22 taken along line VIDxe2x80x94VID of FIG. 6A.
FIG. 7 is an enlarged side view of the in-line type electron gun 29 of FIG. 6A supported on the stem 28 by the electron gun supporting structure 38.
In FIGS. 6A to 6C and 7, reference numeral 31 denotes a cathode, reference character G1 is a beam control electrode, G2 is an accelerating electrode, G3 is a focus electrode, G4 is an anode, and reference numerals 33A and 33B are a pair of bead glasses. The cathode 31, the beam control electrode G1, the accelerating electrode G2, the focus electrode G3 and the anode G4 are coaxially fixed on the pair of bead glasses 33A, 33B with their respective support tabs embedded in the bead glasses 33A, 33B. Reference numeral 291 denotes a shield cup, 32 is a heater, 341, 342 and 343 are stem pins, 35A and 35B are mount supports, 36 is a supporting member, 37 are stem mounds. The same reference numerals as utilized in FIG. 5 designate corresponding elements in FIGS. 6A to 6D and 7.
FIG. 6D is an enlarged cross-sectional view of the neck portion 22 taken along line VIDxe2x80x94VID of FIG. 6A, and illustrates an example of wiring between the stem pins and electrodes of the electron gun. The positions of the respective stem pins are arranged with an equal angular spacing of 25.7xc2x0 on a pin circle of 15.24 mm in diameter, and the stem pins embedded in the respective stem pin positions are connected to the electrodes of the electron gun as shown in Table 1 below.
As is apparent from TABLE 1, a stem pin for applying a high voltage of 5 kV to 10 kV to an electrode such as the focus electrode G3 is spaced by two or more times a regular interval between two adjacent stem pins from adjacent stem pins for applying low voltages to prevent arcing between the high-voltage stem pin and the low-voltage stem pins, and for this reason no stem pins are embedded in the stem pin position #3, #4, #13 and #14.
In FIGS. 6A and 7, only the three stem pins 341, 342, 343 are shown for the sake of clarity, but it will be understood that in practice there are other stem pins for introducing into the neck portion 22 signals such as a video signal and voltages for forming and focusing of the electron beams 30, as explained in connection with FIG. 6D.
In FIG. 7, the cathode 31, the beam control electrode G1, the accelerating electrode G2, the focus electrode G3, the anode G4, the heater 32, and the bead glasses 33A and 33B are the constituent parts of the in-line type electron gun 29, and the stem pins 341, 342, 343, the mount supports 35A, 35B, the supporting member 36 form the electron gun supporting structure 38.
As shown in FIGS. 6B and 7, mounds 37 are formed integrally with a disk portion of the stem 28 at the stem pin positions #1 to #14, and the stem pins including the stem pins 341, 342 and 343 are sealed perpendicularly to and through the disk portion and the mounds 37 of the stem 28 at all the stem pin positions excluding the stem pin positions #3, #4, #13 and #14.
As shown in FIG. 6B, the in-line type electron gun 29 are mounted on the stem 28 such that the pair of bead glasses 33A and 33B indicated by broken lines are parallel with a line connecting the stem pins 341 and 342 embedded at the stem pin positions #11 and #8, respectively. A pair of mount supports 35B and 35A welded to the two stem pins 341 and 342, respectively, are embedded in the bead glass 33A at their ends of the mount supports 35B and 35A. The other bead glass 33B has another mount support 35B embedded therein such that the mount support 35B is positioned symmetrically with the mount support 35A welded to the stem pin 342 with respect to the axis Xxe2x80x94X.
The two mount supports 35B and 35A corresponding to the two stem pins 341, 342 are directly welded to the two stem pins 341, 342 at their respective ends protruding from the bead glass 33A. The mount support 35B embedded in the bead glass 33B cannot be welded directly to any stem pins because no stem pins are embedded in the stem pin positions #3 and #4 near the mount support 35B for prevention of arcing as explained above, and therefore the end of the mount support 35B protruding from the bead glass 33B is welded to the stem pin 343 embedded at the stem pin position #5 via the supporting member 36.
FIGS. 6E and 6F are enlarged perspective views of the mount supports 35A and 35B, respectively.
As shown in FIG. 6C, the supporting member 36 has a generally C-shaped transverse cross section, and comprises a plate-like portion 360 and first and second bent portions 361 and 362 bent in the same direction from the respective sides of the plate-like portion 360. The first and second bent portions 361, 362 are welded to the mount support 35B and the stem pin 343, respectively.
With the electron gun supporting structure 38 of the above configuration, the in-line type electron gun 29 is supported on the stem 28 within the neck portion 22 of the color cathode ray tube.
When the conventional color cathode ray tube is subjected to a great shock, the shock is transmitted to the in-line type electron gun 29 housed within the neck portion 22, and the electron gun supporting structure 38 cannot withstand the increased weight of the in-line type electron gun 29 due to the shock and as a result, the electron gun supporting structure 38 is sometimes deformed such that the in-line type electron gun 29 is deviated from its specified position within the neck portion 22.
FIGS. 8A and 8B illustrate an example of a case where the in-line type electron gun 29 is deviated from its specified position within the neck portion 22, FIG. 8A is a broken-away side view of the neck portion 22 containing the in-line type electron gun 29, and FIG. 8B is an enlarged side view of the deformed supporting member 36.
If the in-line type electron gun 29 is deviated from its specified position within the neck portion 22 as shown in FIG. 8A, chiefly the first bent portion 361 of the supporting member 36 is bent slightly outwardly as indicated by solid lines from its specified position indicated by broken lines in FIG. 8B. As a result, a shield cup 291 nearest to the phosphor screen 24 (see FIG. 5), of the in-line electron gun 29, contacts the inner wall of the neck portion 22 and scrapes off the graphite 50 coated on the inner wall of the neck portion 22. If flakes of the scraped-off graphite 50 lodge fall the in-line type electron gun 29, and become attached to the constituent components of the in-line type electron gun 29, the flakes of the graphite 50 lower the dielectric strength of the in-line type electron gun 29, and cause the in-line electron type electron gun 29 to be defective in dielectric withstand-voltage.
It is true that the supporting strength of the in-line type electron gun 29 by the electron gun supporting structure 38 is increased by bringing closer to the stem mounds 37 the weld points between the stem pins 341, 342 and the mount supports 35B, 35A and the weld point between the stem pin 343 and the second bent portion 362 of the supporting member 36, respectively, but this increases the possibility that cracks occur in the mounds 37 of the stem 28 and consequently, the manufacturing yield rate of the in-line type electron gun 29 is reduced.
The present invention is made in view of the above technical background, and it is an object of the present invention to provide a cathode ray tube capable of increasing the supporting strength of the electron gun without reducing the dielectric strength of the electron gun or lowering the manufacturing yield rate of the electron gun, by using a simple means.
To achieve the above objects, in accordance with an embodiment of the present invention, there is provided a cathode ray tube comprising: a vacuum envelope including a panel portion having a phosphor screen on an inner surface thereof, a neck portion, a funnel portion connecting the panel portion and the neck portion, and a stem closing the neck portion at one end thereof and having a circular array of stem pins sealed therethrough; an electron gun housed in the neck portion, the electron gun including a plurality of electrodes coaxially fixed on a pair of bead glasses; a plurality of mount supports embedded in end portions of the pair of bead glasses for supporting the electron gun on the stem; and a supporting member for connecting one of the stem pins and one of the plurality of mount supports, the supporting member including a plate-like portion, first and second bent portions bent from respective sides of the plate-like portion in a same direction to form a generally C-shaped transverse cross section, the first bent portion being welded to the one of the plurality of mount supports, the second bent portion being welded to the one of the stem pins, and a length of the plate-like portion on a first-bent-portion side thereof in a direction of an axis of the electron gun being longer than a length of the plate-like portion on a second-bent-portion side thereof in the direction of the axis of the electron gun.
With this configuration of the present invention, the entire region of the first bent portion of the supporting member having a generally C-shaped cross section is reinforced by lengthening the length of its plate-like portion in the direction of the electron gun axis, and consequently, even if the electron gun supported by the electron gun supporting structure is subjected to a great shock, the first bent portion of the electron gun supporting structure is capable of sufficiently withstanding the increased weight of the electron gun due to the shock and the electron gun supporting structure is not deformed.
Because the electron gun supporting structure is not deformed and the electron gun is not deviated from its specified position within the neck portion of the cathode ray tube, the graphite coated on the inner wall of the neck portion is not scraped off, and as a result, the dielectric strength of the electron gun is not lowered by the scraped-off graphite attached to the electron gun. Further, the weld points of the stem pins do not need to be brought closer to the mounds of the stem, and consequently, cracks do not occur in the mounds of the stem, or the manufacturing yield rate of the electron gun is not reduced.